Power amplifier tuning and loading device



March 13, 1956 R. J. CASSUTT 2,738,471

O'ER AMPLIFIER TUNING AND LOADING DEVICE Filed April 4, 1952 will IN VEN TOR. 03422; J. (443017- 4r raR/wrr United States Patent POWER AMPLIFIER TUNING AND LOADING DEVICE Russell J. Cassutt, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application April 4, 1952, Serial No. 280,620

1 Claim. (Cl. 336-30) This invention relates in general to a variable inductor, and in particular to a variable inductor in which the number of turns and permeability may be independently adjusted.

It is oftentimes desirable in electronics to have an inductance which may be varied, as for example, in a tuned circuit where a capacitor and inductance are connected together, the frequency may be changed by varying the inductance. At the same time it may be desirable to match the impedance of an output from the tuned circuit so as to match an antenna or other network to which the circuit is connected. This requires that means be provided for varying the impedance.

it is an object of this invention, therefore, to provide an inductor which has a variable output contact and in which the effective inductance may be changed by moving a tuning slug relative to the longitudinal axis of the inductor.

Another object of this invention is to provide an improved variable inductor.

A feature of this invention is found in the provision for a rotatably supported coil form about which a coil is wound and which has a variable core that may be moved longitudinal of the coil to vary its effective inductance.

Further features, objects and advantages of this invention will become apparent from the following description and claim when read in view of the drawings in which:

Figure 1 is a side view of the variable inductor of this invention with a portion of the coil form removed so as to show the internal construction thereof;

Figure 2 is an end view of the variable inductor of this invention;

Figure 3 illustrates the driving means for varying the slug of this invention; and

Figure 4 is a schematic view of this invention.

As shown in Figure 1, a pair of end plates and 11 rotatably support therebetween a coil form 12. One end of the coil form 12 has a conducting axle 13 which is rotatably supported in a suitable bearing 14 mounted in an insulating bracket 16 attached to the end plate 10. The other end of the coil form 12 is formed with a groove 17 into which four rollers 18 are received. The rollers 18 are rotatably supported by the end plate 11 and are equally spaced so as to provide a suitable bearing.

A spiral wire 19 is wound about the coil form 12 intermediate the end plates 10 and 11 and has one end attached to a terminal 21. The terminal 21 is connected to the axle 13 by conductor 22 and a wiper contact 23 engages the end of the axle 13. The contact 23 is supported to the bracket 16 by an insulated mounting 24.

The opposite end of the coil is connected to a band 25 which has a wiper contact 26 connected to it. The wiper contact 26 engages a band 27 supported by the plate 11 about the coil form 12. A terminal 28 connected to the band 27 forms the contact point for one end of the coil.

A roller 29 is rotatably supported on a conductive shaft 31 which has one end supported in a bracket 32. The bracket 32 is attached to the end plate 11. The opposite "ice end of 'thesha'ft 31 passesthrough 'aslot 33 formed inthe end plate 10. A spring 34 is connected to'the shaft 31 and "has its opposite end connectedto the bracket .16. Itiholdsthe roller 29 against the coil 19. The bracket 32 has a terminal-36 at one end thereof from which an electric signal may be removed. "The roller 29 is made of conductive material. The coil form has a gear 37 mounted at one end thereof which meshes with a gear 38 mounted on the output shaft 39 of a driving means 41. Rotation of the coil form moves the roller 29 longitudinally of the coil because of the lead screw action.

The coil form 12 is hollow and receives therein a tuning slug 42 which is attached to a shaft 43. As best shown in Figure 3, the shaft 43 is cut to form a rack 44 which meshes with a pinion 46 driven by a motor 47.

In operation, the position of the roller 29 determines the number of effective turns supplied to the output ter minal 36 and the position of the slug 42 varies the inductance of the coil.

Figure 4 is a schematic diagram of the coil showing the input and output contacts 23 and 28 and the variable pickotf contact 36 which is attached to the roller 29. The slug 42 is driven by the motor 47 and varies the permeability in a well known fashion. The position of the contact 29 varies the impedance and thus, by moving it up and down, various values of impedance may be obtained. This allows an output or input circuit to be efficiently coupled to the coil.

The apparatus of this invention may be used in a circuit where it is desired to control the impedance between two points. For example, suppose a power amplifier is to furnish power to an antenna. It is well known that the load must be matched to the generator for maximum efficiency. Thus, no reflective components are desired. If the generator has a higher impedance than the antenna, it can be connected to terminals 23 and 28 and the antenna may be connected to terminal 36. The opposite side of the antenna may be connected to ground. To vary the impedance ratio for correct matching, the roller 29 is moved relative to coil 19. This forms an autotransformer. To control phasing the slug 42 is moved. This allows the reactive components to be cancelled.

Thus, simultaneous operation of motors 41 and 47 must occur to provide a perfect match between the load and generator. An adjustment of one element necessitates an adjustment of the other.

It is seen that this invention provides means for simultaneously varying the impedance and frequency of a tuned circuit.

Although this invention has been described with respect to a particular embodiment, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claim.

I claim:

An impedance matching inductor comprising a coil form, first and second bearing means located at opposite ends of said coil form, wherein the bearing means rotatably support said coil form, a coil wound on said coil form, first contacting means fastened at one end of said coil form and connected to the adjacent end of said coil, second contacting means fastened to the other end of said coil form and connected to the adjacent coil end, first and second Wiper contacts supported respectively by said bearing means and engaging respectively the first and second contacting means, a rod supported between said bearings substantially longitudinally of and external to said coil form, a roller slideably supported by said rod and engaging said coil, a spring biasing said rod and roller toward said coil form to maintain engagement of said roller with said coil, a first motor, gear transmission means connected between the motor and said coil form said coil, a terminal connected to one end of said rod, a

permeable slug slideably receivable within said coil form independently of rotation of said coil form, and a second motor connected .to actuate the relative position of said slug Within said coil, whereby independent operation of said first and second motors will adjust a Wide range of impedance matching conditions between an input received across the coil and an output received between one end of the coil and the terminal.

Van Yzeren May 27, 1952 

